1. Field of the Invention
The present invention relates to a digital image processing apparatus capable of precisely taking in the image of an original manuscript document having a color background (including or excluding black).
2. Discussion of the Background
Recently, office automation has widely spread throughout the country and all over the world, so that the number of the documents handled in the office has been increasing year by year (day by day). In order effectively to manage those documents, there has been frequently utilized an electronic filing system capable of memorizing the image data obtained by binarily processing the contents of the documents, i.e., the image or information written on the recording paper, by use of an image scanner to produce electronic image data to be stored in the electronic filing system.
In such a filing system, the image scanner frequently employs separation technology to simplify handling of original manuscript documents in which a character area and a picture area exist mixedly and to improve the image quality upon the reproducing the image of the original manuscript document.
Furthermore, as one method of precisely separating an image area into a character area and a picture area using a small amount of hardware, the contents of Japanese Laid-open Patent Publication No. 4-248766 are well known. In the specification thereof, there is disclosed an AND circuit taking a logic AND of the character candidate area detected by a character candidate area detecting circuit and the white background candidate area detected by a white background area detecting circuit. The area judged to be the character candidate area and to be the white background candidate area is considered to be the character area. After practicing the MTF compensation of the above character area, the selection of processing is performed with the priority of the resolution obtained by binarizing with a fixed threshold value. Furthermore, the area outside the area judged to be the above-mentioned character area is considered to be the picture area. In such a method, the selection of processing has been performed with the priority of the halftone obtained by binarizing by use of the dither method or the error diffusion method, and thereby the resolution precessing for the character area and the halftone processing for the picture area could be performed at the same time.
However, the original manuscript document employed in the electronic filing has been paper based not only on a white-background recording paper but also often on a colored-background recording paper such as an article of a newspaper and a magazine, a catalog or brochure, etc. In such situation, according to the above-mentioned binarizing process, since binarizing using a fixed threshold value with the priority of the resolution is practiced only on the circumferential portion of the character contour, the binarizing process is practiced as the picture area by way of the dither method or the error diffusion on the background area. Since the original manuscript document on the colored background is reproduced in the state of the imaginary halftone, the black isolation point lies scattered, and thereby a phenomenon just like a particle-state dirt on the background may apparently happen. Consequently, the reproducing quality of the manuscription document is considerably deteriorated.
Heretofore, the background art regarding the digital image processing apparatus has been described. However, according to such background art, e.g., Japanese Laid-open Patent Publication No. 4-248766, there exists no advantageous functional effect for improving the digital image processing apparatus.
The present invention has been made in view of the above-mentioned problems and other problems in order to solve the above-mentioned defects and troublesome matters of the background arts.
To that end, the present invention provides a high-quality digital image processing apparatus in which the background area in the vicinity of the image area to be treated with the separation processing by use of a image area separation processing mechanism is detected by the background area detecting mechanism, a black isolation point is removed only in the image data existing in the detected background area, such that the black isolation point does not lie scattered at all even on the colored background of the manuscript document.
In a first embodiment of the present invention, a digital image processing apparatus having a function of separating the image data from the original manuscript document into a character area and a picture area is composed of a character candidate area detecting mechanism configured to detect the character candidate area from the image data, a background area detecting mechanism configured to detect the background area in the vicinity of the area to be detected, an area judging mechanism configured to judge that an area satisfying at the same time the conditions of the character candidate area detecting mechanism and the background area detecting mechanism is the character area and the area outside the character area in the picture area, a character processing mechanism configured to process the image data in the character area, a picture processing mechanism configured to process the image data in the picture area, and an area-processing selecting mechanism configured to select either one of the character processing mechanism and the picture processing mechanism on the basis of the judgement result of the area judging mechanism.
In such structure of the digital image processing apparatus as mentioned above, the separation of the image on the original manuscript document having a background density of some extent can be precisely performed.
In a second embodiment of the present invention relating to the first embodiment, the digital image processing apparatus further includes a black isolation point removing mechanism configured to remove the black isolation point only in the image data existing in the background area detected by the background area detecting mechanism among the image data from the processing mechanism selected by the area-processing selecting mechanism.
In such structure of the digital image processing apparatus as mentioned above, the process with the priority of the halftone is practiced in the background area, and the occurrence of the particle-state isolation point is removed. Consequently, the quality of reproducing the original manuscript document can be considerably improved.
In a third embodiment of the present invention relating to the second embodiment, the digital image processing apparatus further includes a black isolation point changing-over mechanism configured to change over the size of the black isolation point removed by the black isolation point removing mechanism. The black isolation point changing-over mechanism changes over the size of the black isolation point removed in accordance with the density of the image data from the original manuscript document.
In such structure of the digital image processing apparatus as mentioned above, the size of the black isolation point to be removed can be changed over in accordance with the contents of the manuscript document image, and thereby the black isolation point of the manuscript document having the background density can be effectively removed. In addition, since the black isolation point removed in accordance with the density of the image data from the manuscript document image can be performed, the quality of reproducing the original manuscript document can be further improved, compared with the case of the second embodiment.